The air suspension to which this invention is applicable typically comprises a bracket secured to and depending from a chassis member of the vehicle, a longitudinal member extending generally lengthwise of the vehicle which is mounted on the bracket for pivoting about an axis generally transverse of the vehicle and which carries an air spring rearwards of the axis so that the air spring acts between the vehicle and the longitudinal member. A stub axle for rotatably mounting a wheel is secured to the member rearwards of the axis. Alternatively, the suspension may comprise two brackets, one depending from each side of the vehicle, each bracket having a longitudinal member extending generally lengthwise of the vehicle and which is mounted to the bracket for pivoting about an axis generally transverse of the vehicle and which carries an air spring rearwards of said front end portion so that the air springs act between the respective longitudinal members and the vehicle. An axle on which is carried two or more road wheels extends between and beyond the longitudinal members and is secured thereto rearwards of said front end portions. Such air suspensions are hereafter referred to as air suspensions of the type described.
Vehicles equipped with an air suspension of the type described are advantageously provided with a lifting system to lift road wheels out of contact with the road surface when their load-carrying capacity is not required, so as to reduce wear of tires and other suspension components. Typically the system will operate to lift a pair of wheels on opposite sides of the vehicle, these wheels either being mounted on a common axle or mounted independently on stub axles.
An example of an air suspension system of the type described having a lifting system is disclosed in EP-A-0 431 673. The lifting system comprises an air bag which is supported on a bracket fixed below a longitudinal member of the suspension, inflation of the air bag urging the longitudinal member upwardly. The system has disadvantages in that the bracket must be welded to a part of the vehicle chassis and a member has to be provided connected between the upper end of the air bag and the longitudinal member at its connection to the axle to control the locus of the top of the air bag.